Pumps are used in numerous applications for transferring a fluid from one location to another. Various categories of pump are available such as centrifugal, rotodynamic and positive displacement, and the choice of pump type for a particular application depends on a number of factors, such as the duty flow rates and pressure requirements, for example. However, much consideration is additionally given to the suitability or compatibility of the pump with the mechanical and chemical properties of the fluid to be pumped. For example, the fluid may be an abrasive suspension of non-soluble particulate material, generally referred to as slurry. Special pumps, known as slurry pumps are available to be used with such slurry material.
One particular form of slurry pump is a centrifugal slurry pump which includes a casing having a suction branch and a delivery branch, and a shaft extending into the casing and being coupled to an impeller at one end, wherein the impeller is located within a pump volute and/or pump casing. In use, a slurry is drawn into the pump casing through the suction branch and through an eye of the rotating impeller. Energy is imparted to the slurry as it is driven in a radial direction through the impeller, with the slurry being discharged from the pump casing via the delivery branch.
In some centrifugal slurry pumps, such as in some lined pumps, for example, a throatbush may be provided between the suction branch and the pump impeller to provide a flow path for a pump fluid, and to define a portion of a pump volute. Such a throatbush is conventionally clamped in place during assembly, which may require additional clamping inserts or the like to be used.
The shaft extends into the casing through a pump casing closure assembly which generally includes an annular plate insert mounted circumferentially about the shaft, wherein the annular plate insert defines a portion of the pump volute, with the remaining portion of the volute being defined by the casing or a casing liner or the like. Conventionally, the annular plate insert is directly and mechanically fixed to the pump casing by means of a number of studs, one end of which are secured to the annular plate and the other end of which extend through apertures in the casing to be bolted thereto. The presence of these studs increase the difficulty and time required to assemble and disassemble a pump due to the requirement for correct alignment of the studs with the apertures in the casing and the need for tooling to bolt the studs to the casing. Additionally, the studs require that the annular insert plate be drilled and tapped to receive the ends of the studs, and likewise may require that the specific points of attachment of the studs to the annular insert plate be of a soft insert material allowing machining. The insert material is conventionally cast or moulded into a wear resistant material which can be metal or rubber. Furthermore, the studs may be exposed to the pump fluid, or the surrounding environment, resulting in corrosion which may affect the integrity of the studs and may cause the studs to seize together with the pump casing, making disassembly difficult and time consuming.
In conventional pumps, a sealing arrangement is provided in combination with the closure assembly to prevent or at least minimise fluid leakage between the shaft and the casing closure assembly conventionally known as a shaft seal. Various types of sealing arrangement are available for use with centrifugal slurry pumps., such as a centrifugal seal, a gland seal or a mechanical seal, which are briefly discussed below.
A conventional centrifugal seal incorporates an expeller which rotates in unison with the impeller in a chamber separated from the volute by the annular plate insert. The chamber is defined between the annular plate insert and an expeller plate secured or clamped between the casing and the annular plate insert. In use, the expeller acts as a turbine to reduce the pressure of the slurry attempting to escape around the back of the impeller.
A gland seal includes a stuffing box located around the shaft and secured or clamped between the annular plate insert and the casing. A number of soft packing rings are located between the shaft and the stuffing box to inhibit fluid transfer therebetween.
A mechanical seal consists of a stationary and a rotating face pressed together under mechanical and hydraulic pressure to prevent leakage. The mechanical seal is held in place around the shaft by a seal holder which is itself secured or clamped between the annular plate insert and the casing. A further description of the form and operation of the various sealing arrangements will be provided hereinafter.
In each type of seal briefly discussed above, limitations are imposed on the size of sealing arrangement which may be utilised due to the presence of the studs used to secure the annular plate insert to the casing, and thus to clamp or secure the respective sealing component between the plate insert and casing. This is particularly the case in centrifugal type seals wherein the presence of the studs makes it difficult to maintain an effective expeller diameter in relation to the impeller diameter to provide sufficient sealing capability.
It is among objects of the present invention to obviate or at least mitigate the aforementioned and other problems with the prior art.